Detrital zircon U-Pb dating of Silurian sandstone in Borohoro area, Western Tianshan Mountains, and its geological implications

The Silurian strata in the Borohoro area on the northern margin of the Yili block in the Western Tianshan Mountains are well exposed and serve as an important carrier for the study of the Early Paleozoic tectonic evolution of the Western Tianshan Mountains. In this paper, sedimentary petrology, geochemistry and LA-ICP-MS zircon U-Pb geochronology were investigated for the Silurian Kuruer Formation sandstone in Shuinichanggou, Nileke County. The result shows that Kuruer Formation was formed in tidalswamp facies. The sandstone in Kuruer Formation is characterized by high LREE, smooth HREE and rather weak negative Eu anomaly. The geochemical characteristics indicate that the sandstone source of Kuruer Formation belongs to the continental arc. According to the U-Pb ages of LA-ICP-MS of 80 detrital zircon grains, the source rocks of Kuruer Formation detrital rocks came from terrains with three different geological periods, mostly 425~510Ma, and subordinately 698~796Ma and 1240~1641Ma, which respectively correspond to the Early Paleozoic, Neoproterozoic and Mesoproterozoic. According to the comprehensive analysis, the Kuruer Formation was formed in Late Silurian and was deposited on the back-arc basin formed by the southward subduction of the North Tianshan Ocean. The material of Kuruer Formation was mainly derived from the northern island arc zone, with the addition of a small amount of materials from the south side of the Yili block.